1. Field of the Invention
The present invention relates to a printer, and more particularly, to a paper pressing force controller of a printer, in which a gap between a transfer roller and a pressing roller can be controlled according to the thickness of a paper sheet.
2. Description of the Related Art
In general, a laser printer prints an image by developing a latent image formed on a photosensitive belt and transferring the developed image to a paper sheet.
FIG. 1 shows a conventional laser printer 10. Referring to FIG. 1, a photosensitive belt 12 is supported by rollers 11a, 11b and 11c and circulates around the rollers 11a, 11b and 11c. An electrostatic latent image is formed on the photosensitive belt 12 by laser scanning units 13, and is developed by developing devices 14. The laser scanning units 13 scan the photosensitive belt 12 with a light beam according to an image to be printed, and the developing devices 14 supply the photosensitive belt 12 with respective developers. In the case of a color printer, the color printer may be provided with a plurality of developing devices 14 and laser scanning units 13 corresponding to the respective colors, i.e., yellow (Y), magenta (M), cyan (C) and black (B).
The developed image on the photosensitive belt 12 is transferred to a transfer roller 15, and the transferred image is printed on a paper sheet 17, supplied from guide rollers 16, between the transfer roller 15 and a pressing roller 18.
The pressing roller 18 is elastically biased against the transfer roller 15 at a constant pressure by a spring 19a fixed to a supporter 19b. Therefore, constant pressure is exerted on the paper sheet 17 supplied between the transfer roller 15 and the pressing roller 18.
Thus, in a conventional printer, the pressing roller 18 is pressed at a constant pressing force by the spring 19a without reference to the thickness of a supplied paper sheet. Therefore, when a paper sheet 17 is thick, the constant pressure of the pressing roller 18 is transferred to the photosensitive belt 12 via the transfer roller 15, and the developed image may become distorted.